The U.N. must act to stop the violence in Syria, a major conference heard Sunday as bloodshed on the ground claimed more lives.

The head of the Arab League Nabil al-Arabi called on participants of the "Friends of Syria" conference to "simultaneously call on the Security Council to take a binding decision ... to stop the violence in Syria."

Turkish Prime Minister Recep Tayyip Erdogan arrived in Tehran on Wednesday for a two-day visit focused on talks about Iran's nuclear policy and ties, the official IRNA news agency reported.

Erdogan, who was greeted at the airport by Iranian Foreign Minister Ali Akbar Salehi, flew in from South Korea, where he had attended a nuclear security summit with other world leaders including U.S. President Barack Obama.

Hundreds of Syrian opponents gathered in Istanbul Tuesday to envision a "democratic" state in Syria, seeking to prepare for the eventual aftermath of President Bashar Assad's era.

A large number of opposition factions gathered behind closed doors in the Turkish city to discuss the basic principles for a future Syrian state, which the Syrian National Council (SNC), the umbrella opposition, has pledged to be multinational, civil and democratic.

Turkish ex-army chief Ilker Basbug on Tuesday rejected terrorism charges against him and refused to mount a defense in his trial for seeking to overthrow the government, the Anatolia news agency said.

"I am astounded at being accused of leading a terrorist organization," the retired general told a court in Silivri, outside Istanbul, where his trial opened Monday.

Several Syrian opposition groups will gather in Turkey on Monday to hammer out common objectives in the face of the regime's deadly crackdown on dissent, the main umbrella grouping said.

The Istanbul meeting comes ahead of the second "Friends of Syria" conference in the same city on April 1, the Syrian National Council said in a statement on Saturday.

Turkey said Tuesday it was bringing forward by a day to April 1 a "Friends of Syria" conference in Istanbul, designed to pressure the Damascus regime into halting its crackdown on opponents.

"We have decided to bring the meeting forward for technical reasons," a Turkish diplomat said of the gathering originally set for April 2.

Thousands of Kurds clashed with police Sunday in Istanbul and the southern city of Diyarbakir, leaving nine people injured as security forces tried to stop Kurdish New Year festivities.

Police fired tear gas and water cannon to prevent more than 40,000 Kurds from gathering at the main square in Diyarbakir, capital of the Kurdish-majority south, an Agence France Presse correspondent said.

Hamas leader Khaled Meshaal arrived in Turkey on Friday to meet with Prime Minister Recep Tayyip Erdogan, who advocates cooperation with the Islamist movement, a close aid to the premier said.

"The prime minister will meet with Meshaal at 2:00 pm (1200 GMT)," the source told AFP on condition of anonymity.

A new Turkish blockbuster glorifying the 15th-century Ottoman conquest of Constantinople has taken Turkey by storm at a time when the government is flexing its muscles as a new regional strongman.

"Fetih 1453" -- or Conquest 1453 -- has drawn record crowds since it opened on February 16, recounting what is upheld as one of the most glorious moments in the nation's history.

A remote-controlled roadside bomb wounded 16 people, mostly policemen, when it exploded near a passing police bus in the center of Istanbul on Thursday, Turkish authorities said.

"It appears to be a remote-controlled bomb that went off as a duty vehicle with 21 policemen on board drove by," Istanbul police chief Huseyin Capkin told the Anatolia news agency.